(a) Field of the Invention
The present invention relates to a random access method based on the number of messages and, more particularly, to a random access method based on the number of messages transmitted per frame.
(b) Description of the Related Art
In general, a mobile wireless system performs uplink random access by using a binary exponential backoff (BEB) scheme. A collision generated in performing uplink random access is resolved based on an initial backoff window and a maximum backoff window controlled by a base station.
In the mobile wireless system, a terminal that wants to request a bandwidth detects the values of the initial backoff window and the maximum backoff window from an uplink channel descriptor (UCD) message. In this case, the values of the initial backoff window and the maximum backoff window indicate the multiplier of 2. For example, when a value detected from the UCD message is 4, the initial backoff window is 0 and the maximum backoff window is 15, so the backoff window has values between 0 and 15, and when a value detected from the UCD message is 10, the initial backoff window is 0 and the maximum backoff window is 1024, so the backoff window has values between 0 and 1024.
Acquiring the values of the backoff window in this manner, the terminal randomly selects one of the values of the backoff window. Here, the value selected by the terminal refers to the number of slots at a contention interval to be transmitted by the terminal before the terminal transmits a bandwidth request message. After transmitting the bandwidth request message, the terminal waits to receive a bandwidth permission message from a continued MAP.
When the bandwidth permission message is received, the terminal terminates the bandwidth requesting procedure. However, if the bandwidth permission message fails to be received within a predetermined time, the terminal determines that the bandwidth request procedure has failed. And, the terminal increases the backoff window by a certain multiple within a range in which the backoff window does not exceed the maximum backoff window. When the bandwidth request is not successful in spite of the fact that the process is attempted by a maximum repeated number of times, the terminal discards a corresponding protocol data unit.
In this manner, the collision solution in case of using the related art BEB scheme is controlled by a base station and is performed irrespective of the number of uplink random accesses, which results in problems in that the probability of the collision of the uplink random accesses increases depending on the number of terminals that perform the uplink random access request and an uplink access delay increases.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.